Big ass mother-in-law, she wants to have sex with me every day, her male doesn't satisfy her

My mother-in-law, we met recently since my girlfriend introduced us to her family recently, for some reason I realized that my mother-in-law liked me and little by little we were able to live more with her and me, I asked her for her number to be more discreet and a few days later, I told her that she was very beautiful and attractive, She told me that nothing could happen because she was with my girlfriend, but she also admitted that she liked me a lot, a week later she started us to drink wine and we have had hard sex since then, she tells me that she had a lot of desire since she met me since her husband does not comply with her